Implement OpenGL backend in Android viewer app

tools/viewer/sk_app/android/Window_android.cpp

Index: tools/viewer/sk_app/android/Window_android.cpp
diff --git a/tools/viewer/sk_app/android/Window_android.cpp b/tools/viewer/sk_app/android/Window_android.cpp
index 4f33870c1ae225e122215e579b0295d0fa4493ec..1c46d98178ad5808e22a7893053363b259d5f276 100644
--- a/tools/viewer/sk_app/android/Window_android.cpp
+++ b/tools/viewer/sk_app/android/Window_android.cpp
@@ -6,8 +6,8 @@
 */
 
 #include "Window_android.h"
-
-#include "VulkanWindowContext_android.h"
+#include "../GLWindowContext.h"
+#include "../VulkanWindowContext.h"
 
 namespace sk_app {
 
@@ -46,26 +46,42 @@ void Window_android::setUIState(const Json::Value& state) {
 }
 
 bool Window_android::attach(BackendType attachType, const DisplayParams& params) {
-    if (kVulkan_BackendType != attachType) {
+    if (kVulkan_BackendType != attachType && kNativeGL_BackendType != attachType) {

[jvanverth1, 2016/06/02 17:17:36]

You can probably remove this block -- the conditional always evaluates to false.

[liyuqian, 2016/06/02 18:47:13]

Done.

         return false;
     }
 
+    fBackendType = attachType;
     fDisplayParams = params;
 
-    // We delay the creation of fTestContext until Android informs us that
+    if (fNativeWindow) {
+        initDisplay(fNativeWindow);

[scroggo, 2016/06/02 18:25:17]

nit: Skia code calls member functions using "this", e.g.

this->initDisplay(fNativeWindow);

[liyuqian, 2016/06/02 18:47:13]

Done.

+    }
+    // If fNativeWindow is not set,
+    // we delay the creation of fWindowContext until Android informs us that

[scroggo, 2016/06/02 18:25:16]

When/where does that happen? Should we return false here?

[liyuqian, 2016/06/02 18:47:13]

It happens in initDisplay, which is initiated by kSurfaceCreated event. Derek
originally wrote this function by returning true so I just followed his design.
I'll update the comment to make it more clear.

     // the native window is ready to use.
     return true;
 }
 
 void Window_android::initDisplay(ANativeWindow* window) {
     SkASSERT(window);
+    fNativeWindow = window;
     ContextPlatformData_android platformData;
     platformData.fNativeWindow = window;
-    fWindowContext = VulkanWindowContext::Create((void*)&platformData, fDisplayParams);
+    switch (fBackendType) {
+        case kNativeGL_BackendType:
+            fWindowContext = GLWindowContext::Create((void*)&platformData, fDisplayParams);
+            break;
+
+        case kVulkan_BackendType:
+        default:

[scroggo, 2016/06/02 18:25:16]

Why does default create a vulkan backend?

[liyuqian, 2016/06/02 18:47:13]

Because that's the first backend in Android viewer app?

[scroggo, 2016/06/02 18:58:37]

It looks like there are only two enum values. Can you just remove "default"
entirely? That way, if we add another enum, the compiler will catch us if we
forget to add another case.

Another option would be to default to SkASSERT(false); I think you only want to
create a vulkan backend for kVulkan_BackendType

+            fWindowContext = VulkanWindowContext::Create((void*)&platformData, fDisplayParams);
+            break;
+    }
 }
 
 void Window_android::onDisplayDestroyed() {
     detach();
+    fNativeWindow = nullptr;
 }
 
 void Window_android::onInval() {